Certain genes may play a role in the cellular response to stress or DNA-damaging agents. For example, metallothionein I and II, collagenase, and plasminogen activator are induced after UV irradiation (Angel, et al., 1986; 1987; Fornace, et al., 1988a and b; Miskin, et al., 1981). B2 polymerase III transcripts are increased following treatment by heat shock (Fornace, et al., 1986; 1989a). Furthermore, although the level of DNA polymerase β mRNA is increased after treatment with DNA-damaging agents, this transcript is unchanged following irradiation, suggesting that specific DNA-damaging agents differentially regulate gene expression (Fornace, et al., 1989b). Protooncogene c-fos RNA levels are elevated following treatment by UV, heat shock, or chemical carcinogens (Andrews, et al., 1987; Hollander, et al., 1989a). In this regard, the relative rates of fos transcription during heat shock are unchanged, suggesting that this stress increased c-fos RNA through posttranscriptional mechanisms (Hollander, et al., 1989b).
Investigations of the cytotoxic effects of ionizing radiation has focused on the repair of DNA damage or the modification of radiation lethality by hypoxia (Banura, et al., 1976; Moulder, et al., 1984). In prokaryotes and lower eukaryotes, ionizing radiation has been shown to induce expression of several DNA repair genes (Little, et al., 1982); however, induction of gene expression by ionizing radiation has not been described in mammalian cells. DNA-damaging agents other than x-rays induce expression of a variety of genes in higher eukaryotes (Fornace, et al., 1988, 1989; Miskin, et al., 1981).
What is known about the effects of ionizing radiation is that DNA damage and cell killing result. In many examples, the effects are proportional to the dose rate. Ionizing radiation has been postulated to induce multiple biological effects by direct interaction with DNA or through the formation of free radical species leading to DNA damage (Hall, 1988). These effects include gene mutations, malignant transformation, and cell killing. Although ionizing radiation has been demonstrated to induce expression of certain DNA repair genes in some prokaryotic and lower eukaryotic cells, little is known about the effects of ionizing radiation on the regulation of mammalian gene expression (Borek, 1985). Several studies have described changes in the pattern of protein synthesis observed after irradiation of mammalian cells. For example, ionizing radiation treatment of human malignant melanoma cells is associated with induction of several unidentified proteins (Boothman, et al., 1989). Synthesis of cyclin and coregulated polypeptides is suppressed by ionizing radiation in rat REF52 cells but not in oncogene-transforned REF52 cell lines (Lambert and Borek, 1988). Other studies have demonstrated that certain growth factors or cytokines may be involved in x-ray-induced DNA damage. In this regard, platelet-derived growth factor is released from endothelial cells after irradiation (Witte, et al., 1989).
Initiation of mRNA synthesis is a critical control point in the regulation of cellular processes and depends on binding of certain transcriptional regulatory factors to specific DNA sequences. However, little is known about the regulation of transcriptional control by ionizing radiation exposure in eukaryotic cells. The effects of ionizing radiation on posttranscriptional regulation of mammalian gene expression are also unknown.
Many diseases, conditions, and metabolic deficiencies would benefit from destruction, alteration, or inactivation of affected cells, or by replacement of a missing or abnormal gene product. In certain situations, the affected cells are focused in a recognizable tissue. Current methods of therapy which attempt to seek and destroy those tissues, or to deliver necessary gene products to them, have serious limitations. For some diseases, e.g., cancer, ionizing radiation is useful as a therapy. Methods to enhance the effects of radiation, thereby reducing the necessary dose, would greatly benefit cancer patients. Therefore, methods and compositions were sought to enhance radiation effects by investigating effects of radiation on gene expression. A goal was to provide new types of therapy using radiation, and to explore other uses of radiation.